Current knee arthroplasty systems require specialized instruments of many varieties for the purposes of, for example, treating left and right knees, referencing either the anterior or posterior portion of a femur to align an implant, accommodating many different sizes, and matching many different degrees of external rotation. Various combinations of instruments purposed in these many different ways can lead to very large sets of instruments required to accomplish even the one basic task of aligning a femoral component on a patient's femur. Additionally, femoral cutting blocks used in many current knee arthroplasty systems are typically provided in multiple varieties and sizes. Providing cutting blocks of multiple varieties and sizes can contribute significantly to the bulk of current knee arthroplasty systems because cutting blocks are typically relatively heavy and can be very numerous in cases where an instrument set is designed to support implantation of a large number of sizes of knee arthroplasty components. As should be appreciated, large instrument sets are expensive to manufacture, expensive to ship, cumbersome to handle, time and cost intensive to clean and sterilize, and may be more complicated to learn to use effectively.
A single instrument or reduced number of instruments and related techniques designed and configured to accomplish multiple ones of the above-discussed purposes could therefore reduce costs, improve efficiency, and improve overall results. Such a single instrument or reduced number of instruments may also reduce or eliminate the need to change instruments intraoperatively.
In instances where a surgeon would like to switch between an anterior referencing technique and a posterior referencing technique intraoperatively, a single instrument with features applicable and valuable to each technique would be beneficial. An anterior referencing technique makes primary spatial reference to the anterior cortex of a patient's femur, and anterior resection is fixed while posterior resection varies with implant size. Because a femoral component is typically positioned generally flush against the anterior cortex, an anterior referencing technique enables reapproximation of the patellofemoral joint. An anterior referencing technique also reduces the chance of notching the anterior cortex of a patient's femur. One disadvantage associated with an anterior referencing technique is that such techniques may tend to lead to a patient's treated knee being loose in flexion. A posterior referencing technique makes primary spatial reference to a patient's posterior femoral condyles, and posterior resection remains constant while anterior resection varies with respect to the anterior cortex of the femur. Therefore, the posterior resection will equal the posterior thickness of the prosthesis, thereby resulting in a balanced flexion-extension space. One disadvantage associated with a posterior referencing technique is that such techniques may lead to overstuffing of the patellofemoral joint and notching of the anterior cortex of the femur.
In cases where a surgeon would like to intraoperatively reduce the size of the femoral component being used for one or more reasons, and a posterior referencing technique is being used, a better clinical result may sometimes be achieved by switching from a posterior referencing technique to an anterior referencing technique. Such implant downsizing accomplished during a posterior referencing technique alone is very likely to lead to notching of the anterior cortex of the femur. An improved instrument or instrument set and related techniques may provide a surgeon with the option of transitioning from a posterior referencing technique to an anterior referencing technique with little or no change to the associated instrumentation.
Additionally, current knee arthroplasty systems include separate cutting blocks for use with anterior referencing techniques and posterior referencing techniques. Cutting blocks having multiple applications associated with various uses of a knee arthroplasty instrument set would reduce the number of instruments in the instrument set, and would therefore address some of the limitations of currently available instrument sets. For example, cutting blocks that may be used in both anterior and posterior referencing techniques have the potential to significantly reduce the number of cutting blocks required in an instrument set.